The present invention relates to an apparatus and method for the plasma treatment of a substrate and more particularly to a method and apparatus for the selective plasma treatment of isolated portions of a filament.
It is critical that catheters for balloon angioplasty, other cardiovascular or other. non-cardiovascular procedures have an absolutely secure bond between the catheter tube and the balloon. The same is true with regard to other devices which may be attached to the tube, such as EKG electrodes, sensors of ions, pressure, temperature, oxygen and/or carbon dioxide concentrations, blood flow and the like. The attachment of the balloon or other device is typically achieved by use of an epoxy resin which bonds the device to the outside of the catheter filament. Such devices often do not bond well to common catheter filament materials such as polyethylene, Teflon.RTM., silicone, polyurethane and the like. Inadequate bonding between the catheter and the attached instrument can result in detachment and release of the instrument into the blood stream of the patient, which can, in turn, interfere with its operation and possibly result in serious injury or death.
Adhesion of balloons and other devices to the surface of the catheter filament may be improved by plasma etching prior to attachment with epoxy resin. However, such treatment also increases the affinity of the entire surface of the catheter for blood platelets and the like. Adherence of blood platelets to the catheter filament can block the flow of blood around or through the catheter It is important, therefore, to improve the adhesion characteristics of the catheter where the instrument is attached without increasing the platelet affinity of those other areas of the catheter filament surface (interior and exterior) that will be exposed to the blood.
Some devices attached to catheter filaments may occupy the entire circumference of the catheter filament at a given location and thus are bonded along the entire circumference In this instance, it is desirable to provide maximum adhesion characteristics for a predetermined segment of the filament, the segment comprising the entire circumference of the catheter filament along a particular length of the filament. Other devices occupy less than the entire circumference of the filament. In the latter case, it is preferable to enhance adhesion characteristics only for that lesser portion of the filament surface to which the device is attached.
The hollow interiors of catheters are sometimes used to transport blood during angioplasty. Thus, it may also be important to avoid increasing the platelet affinity of the interior surface of the catheter. It also may be desirable to provide a surface treatment to the interior surface of the catheter. Some catheters may comprise multiple interior passages or cavities For these multi-barrel catheters, it may be desirable to provide surface treatment to one or more interior passages while preventing the surface treatment of one or more other interior passages.
Of methods heretofore available for improving the adhesion characteristics of filament surfaces, none are wholly satisfactory for catheter applications. These methods for the most part are slow and awkward, require extensive preparation of the workpiece, or yield results which are not highly reproducible. These procedures undesirably rely upon the operator's training and dexterity and are vulnerable to operator fatigue.
One such method involves etching of the filament surface with the corona of a high voltage electrical conductor. This technique, however, is imprecise due to the lack of operator control over the arc between the electrode and the workpiece, as well as to the presence of gaseous species at the workpiece surface. This method is also limited by the operator's inability to use precise concentrations of gases to improve bonding sites. It is therefore difficult to chemically treat a precise and predetermined portion of the filament surface.
Mechanical and chemical etching techniques are likewise imprecise. Chemical etching processes employ toxic chemicals which are hazardous to operators and to the environment, are very non-selective, require burdensome piecewise masking of those filament regions which are not to be treated prior to application of the etchant, and require burdensome manual removal of masking mechanisms.
Accordingly, a need has existed for a method of selectively improving the adhesion characteristics of predetermined portions of a catheter filament surface, the method being environmentally safe, reproducible and less labor-intensive than currently used methods.